As disclosed in Japanese Unexamined Patent Gazette No. H09-210515, there is a conventional refrigeration system which is formed into a two-stage cascade refrigerating cycle of the vapor compression type by connecting together a high temperature-side refrigerant circuit and a low temperature-side refrigerant circuit through a refrigerant heat exchanger. More specifically, the high temperature-side refrigerant circuit, on the one hand, comprises a closed circuit formed by sequential connection, established by refrigerant piping, of a compressor, a heat source-side heat exchanger, an expansion valve, and an evaporation portion of a refrigerant heat exchanger. On the other hand, the low temperature-side refrigerant circuit comprises a closed circuit formed by sequential connection, established by refrigerant piping, of a compressor, a condensation portion of the refrigerant heat exchanger, an expansion valve, and an application-side heat exchanger.
Such a two-stage cascade refrigerating cycle refrigeration system finds applications in refrigerating apparatus such as showcases for foods or the like installed at stores (e.g., super markets and convenience stores). Defined in such a showcase are a display space for frozen foods in the showcase chamber and an air passage for the circulation of air with the display space. The application-side heat exchanger, which is disposed in the air passage, is able to provide a supply of air into the showcase chamber with the aid of an air blower.
During the operation of the showcase, refrigerants are circulated in the high temperature-side refrigerant circuit and in the low temperature-side refrigerant circuit, wherein heat exchange is carried out between the refrigerants of these two refrigerant circuits in the refrigerant heat exchanger. With regard to the low temperature-side refrigerant circuit, a refrigerant discharged out of the compressor condenses in the refrigerant heat exchanger, decompresses in the expansion valve, and thereafter evaporates by heat exchange with air flowing through the air passage in the application-side heat exchanger in the showcase, whereby the air is cooled. Then, the cooled air is supplied, through the air passage, into the display space in the showcase chamber. In this way, foods are preserved at a predefined low temperature to maintain their freshness.
However, in such a conventional showcase constructed in the way described above, the operation will be brought into a stop when there occurs a failure in some equipment on the heat source side (e.g., the compressor), even though the application-side equipments are normally operating. There are some possible means of coping with such stoppage, one of which is to transfer the goods to another showcase that remains in operation. This, however, results in an increase in the load of refrigerating/cooling, therefore producing the problem of making it impossible to maintain the quality of goods at a satisfactory level. Particularly, in the case a freezing showcase stops, this produces the problem that the stored goods cannot be preserved at a satisfactory level of quality even when transferred into a cold storage showcase.
Bearing in mind the above-described problems, the present invention was made. Accordingly, an object of the present invention is to maintain the quality of goods by achieving continuation of refrigeration operation even when a heat source-side equipment stops in a two-stage cascade refrigerating cycle refrigeration system applied to a showcase or the like.